Could Teen Marijuana Use Cause Permanent Brain Damage?

According to the results of a study from the Northwestern University Feinberg School of Medicine in Chicago, heavy marijuana abuse during adolescence could cause permanent damage to the parts of the brain associated with working memory, or the ability to retain and use information in the moment and then commit it to long-term memory.

The study, published in the journal Schizophrenia Bulletin, compared young adults who have a history of adolescent marijuana use with young adults who have no adolescent history of heavy marijuana use. Researchers found abnormalities in the brains of those with a history of adolescent marijuana use.

Adolescent Marijuana Use Causes Brain Changes Similar to Schizophrenia

Researchers used MRI scans to examine specific parts of the brains of young people with a history of heavy marijuana use in adolescence, where “heavy use” is defined as having used the drug every day for at least three years.

The study looked at the brains of 44 healthy controls with no history of marijuana use as well as the brains of 10 young people with a history of marijuana use, 15 with a combined history of marijuana use and a schizophrenia diagnosis, and 28 with a schizophrenia diagnosis but no history of marijuana use.

A history of cannabis use has been found to be more common in people diagnosed with schizophrenia than in the general population.

The researchers found those young people who had used marijuana heavily during adolescence showed brain abnormalities in the thalamus, the part of the brain associated with cognitive input; the striatum, the part associated with motivation and reward, and also implicated in addiction; and in the globus pallidus, a part that plays a role in memory and movement.

Specifically, the structures appeared to researchers to collapse and shrink. It’s believed this may denote a decrease in the number of neurons in these parts of the brain.

Heavy Marijuana Abuse in the Teen Years Could Cause Lasting Damage

When study participants were asked to perform tests of working memory, like remembering sequences of numbers they’d just seen, those with a history of heavy marijuana use performed poorly compared to the healthy controls and those with schizophrenia and no history of marijuana use.

The heavy marijuana users had been marijuana-free for at least two years at the time of the study, proving the brain changes do not correct themselves even with long-term abstinence from marijuana.

However, the study does not make clear whether the brain changes found in the former heavy marijuana users occurred as the result of marijuana use, or whether they predate the marijuana use. It’s possible that the brain abnormalities made the test subjects more susceptible to heavy cannabis use, rather than occurring as the result of a cannabis use.

Researchers did find that those subjects who began using marijuana heavily at a younger age experienced more severe brain abnormalities, so this could suggest that marijuana use caused the abnormalities and not the other way around.

Further Proof That Marijuana Abuse Increases Schizophrenia Risk

The brain changes caused by chronic marijuana abuse are similar to the changes caused by schizophrenia, researchers found. The precise link between schizophrenia and heavy marijuana use is still not fully understood, but it’s believed heavy marijuana use could contribute to the development of the disease in those already at risk for it.

Ninety percent of the schizophrenic marijuana abusers in this study have a history of heavy marijuana use that predates the onset of their schizophrenia symptoms. Risk factors for schizophrenia include a family history of the disease.

Subjects with a history of marijuana use displayed many of the same brain changes regardless of whether or not they had been diagnosed with schizophrenia. Subjects with schizophrenia and a history of chronic marijuana abuse displayed more severe damage to the thalamus, a part of the brain crucial to learning, memory and transferring information between different parts of the brain.

According to a recent study from Northwestern University, long-term heavy marijuana use could cause lasting damage to the parts of the brain associated with working memory.

Memory impairments associated with marijuana abuse could last for years even after heavy substance abuse ends. The brain damage caused by heavy marijuana use could be a contributing factor in the development of schizophrenia.

About the Author: Contributing blogger Laura Monaghan was inspired to become an addiction counselor with RehabHotline.orgafter seeing firsthand the damage addiction can do to families.